Additionally, tanks for storing products are known which are equipped with a sensor for measuring the level of the product contained in the tank and with an associated controller for transmitting a warning signal to a restocking centre of the supplier. This controller compares the level values output by the sensor with a preset threshold and transmits, should the measured value be less than the threshold, a warning signal to the restocking centre.
Although this solution solves the abovementioned point (1) by replacing human intervention by a sensor associated with a controller, it still requires a high warning threshold to be able to comply with the abovementioned delivery deadlines. Consequently, optimization of restocking is far from being guaranteed, given that the choice of a high warning threshold, necessary for leaving a safety margin, is prejudicial thereto, and that the forecast of the delivery requirements is inaccurate and difficult to obtain. Moreover, to avoid a depletion of stock at the customer's premises, the supplier is often led to install oversized storage tanks, thus increasing on the one hand the product distribution cost and on the other hand the dimensions of the tank at the customer.
It is also known to use forecasting software which utilizes the dates and the quantities delivered per storage facility which are entered manually into a database by the supplier on returning from the deliveries. As before, a restocking threshold is set. The program extrapolates the known consumption figures so as to calculate the date on which the product storage level is liable to drop below this threshold. This date serves to schedule the supplier's delivery rounds.
Given that the information is entered manually, this solution is unreliable since transcription errors or data entry omissions are easily made. Following such an error, the supplier forecasts deliveries either too early which turns out expensive for him since the quantity of product delivered per trip is small, or else too late, which may lead to a depletion of stock and have serious consequences for the customer.
Furthermore, this approach is based only on the product quantities consumed and involves no knowledge of the actual levels of the stockpiles. Given that the storage level is read off only on the occasions of deliveries, this approach does not make it possible to react to exceptional situations which arise for example when a customer decides to operate his plant during a weekend or when working additional exceptional hours. In this case, the software forecasts a lower consumption than the actual consumption and this may lead to a depletion of stock if there is no human intervention. Consequently, the delivery dates calculated by this software may lead the supplier into error in the scheduling of the rounds of his vehicles. In order, nevertheless, to be able to ensure continuity of supply, the restocking threshold must therefore not only take account of the delivery deadline but also of any variations in the product quantities consumed which cannot be taken into account by this approach.
Owing to this uncertainty, this approach is generally applied in a very conservative manner with high safety thresholds, which hinders optimization of restocking per vehicle trip, and may lead the supplier to install oversized tanks at the customer's premises.
Additionally, the log of consumption on the basis of which the forecasts for the entire pool of stockpiles are made is generally recorded in a centralized databank or centralized file. The system is therefore vulnerable to a loss of data.
The invention aims to alleviate these various drawbacks by proposing a process and a device for implementing the process, which make it possible to generate an early warning signal with the aid of which the supplier can more accurately forecast the date of restocking a tank with a view to optimizing the restocking of a pool of storage tanks.
To this end, the subject of the invention is a process for generating at least one warning signal relating to the level in a tank for storing a product with a view to the restocking of the tank, in which a, least one measurement sensor associated with the tank is used to determine, at successive instants t.sub.0, t.sub.1 . . . t.sub.i-1, t.sub.i respectively, the values N.sub.0, N.sub.1 . . . N.sub.i-1, N.sub.i of the level of storage of the product in the tank, together with the values of the quantity of product .DELTA.N.sub.1, .DELTA.N.sub.2, . . . .DELTA.N.sub.i-1, .DELTA.N.sub.i consumed during the time intervals defined by two successive instants .DELTA.t.sub.1 =t.sub.1 -t.sub.0, .DELTA.t.sub.2 =t.sub.2 -t.sub.1, . . . .DELTA.t.sub.i-1 =t.sub.i-1 -t.sub.i-2, .DELTA.t.sub.i =t.sub.i -t.sub.i-1, characterized by the following steps:
the measured values N.sub.0, N.sub.1, . . . N.sub.i-1, N.sub.i, together with .DELTA.N.sub.1, .DELTA.N.sub.2, . . . .DELTA.N.sub.i-1, .DELTA.N.sub.i and the associated measurement instants t.sub.0, t.sub.1 . . . t.sub.i-, t.sub.i are placed in memory, PA0 at successive instants .tau..sub.0, .tau..sub.1 . . . .tau..sub.j-1, .tau..sub.j which are spaced apart by time intervals .DELTA..tau..sub.1 =.tau..sub.1 -.tau..sub.0, .DELTA..tau..sub.2 =.tau..sub.2 -.tau..sub.1, . . . .DELTA..tau..sub.j =.tau..sub.j -.tau..sub.j-1 respectively, the time intervals .DELTA..tau. being predefined and their duration being greater than or equal to the time intervals .DELTA.t.sub.n, n being any natural number lying between 0 and i, the values placed in memory of the product quantity consumed .DELTA.N.sub.n during the time intervals .DELTA.t.sub.n are used to calculate a value of the estimated quantity of product C.sub.k which will be consumed between the instant .tau..sub.j and the instant .tau..sub.j+k, .tau..sub.j+k being the k-th instant following .tau..sub.j and spaced apart therefrom by the time interval .delta..tau..sub.k =.DELTA..tau..sub.j+1 +.DELTA..tau..sub.j+2 + . . . +.DELTA..tau..sub.j+k, PA0 this value C.sub.k is subtracted from the most recent measured value N.sub.i so as to obtain an estimated value N.sub.i -C.sub.k of the storage level at the instant .tau..sub.j+k, PA0 this estimated value N.sub.i -C.sub.k of the storage level is compared with a preset threshold .theta., and PA0 a warning signal is generated if the estimated value N.sub.i -C.sub.k is less than the preset threshold .theta.. PA0 the values of the product quantity .DELTA.N.sub.n consumed during the time interval .DELTA.t.sub.n are determined by subtracting the value N.sub.n of the storage level measured at the instant t.sub.n from the value N.sub.n-1 of the storage level measured at the instant t.sub.n-1, PA0 the value of the product quantity .DELTA.N.sub.n consumed during the time interval .DELTA.t.sub.n is determined by measuring by means of a second sensor the flow rate of product drawn off from the tank and by integrating this measured flow rate between the instants t.sub.n-1 and t.sub.n.
The process according to the invention can moreover comprise one or more of the following characteristics:
The subject of the invention is also a device for generating at least one warning signal making it possible to implement the process defined above, characterized in that it comprises means for measuring the storage level of the product, a central processing unit for utilizing the level read off by the measurement means, a memory linked to the central processing unit and intended for holding the measurement instants t.sub.n output by a clock, the storage levels of the product N.sub.n in the tank and the product quantities N.sub.n consumed during the time intervals .DELTA.t.sub.n, means for placing in memory at least one storage level threshold .theta., means for comparing the value of the storage level N.sub.i -C.sub.k at the future instant .tau..sub.j+k output by the central processing unit with the said threshold .theta., and means for generating a warning signal which are controlled by the comparison means.
The subject of the invention is also a tank for storing a product, characterized in that it comprises a device of the type defined above.